void main(){

  //定义为num类型，可以在 int double 之间转换
  num a = 10;

  a = 10.5;

  //定义为int类型，不能默认赋值为double
  int b = 20;
//  b = 20.5;

  //定义为double类型，不能默认赋值为int
  double c = 20.5;
//  c = 20;

  int aa = 10;
  double bb = 10.5;

//  print(aa + bb);
//  print(aa - bb);
//  print(aa * bb);
//  print(aa / bb);
//  print(aa ~/ bb);
//  print(aa % bb);

//    print(0.0 / 0.0);

    int d = 10;
    print(d.isNaN);
    //是否是奇数
    print(d.isOdd);
    int e = 11;
    //是否是偶数
    print(e.isEven);


    int f = -100;
    print(f.abs());
    double g = 10.5;
    //四舍五入
    print(g.round());
    //不大于本数的最大值
    print(g.floor());
    //不小于本数的最小值
    print(g.ceil());

    print(g.toInt());

    int h = 20;
    print(h.toDouble());

}